1. Field of the Invention
The present invention relates to an electron beam exposure apparatus used for the exposure process of a semiconductor integrated circuit or the like, an electron projecting lens suitable for the electron beam exposure apparatus, and a device manufacturing method.
2. Description of the Related Art
In recent years, electron beam exposure apparatuses have been under development for the purpose of improving the accuracy and productivity of microdevices such as semiconductor devices. As one technique of electron beam exposure, a pattern to be transferred onto a sample is divided into a plurality of divisions, and the plurality of divisions is formed on a mask. The mask is irradiated with an electron beam, and simultaneously, the mask stage on which the mask is placed is continuously moved in one direction such that the sample is irradiated with the electron beam transmitted through the mask. According to this technique, since the electron beam irradiation area can be made wider than that of a conventional electron beam exposure technique using the partial full exposure method, improvements in both resolution and mass productivity can be expected.
Normally, an electron projecting lens having a magnetic doublet lens is used for the projecting system. A stop for separating scattered electrons at the pattern portion of the transfer mask from unscattered electrons at the mask membrane portion is disposed at a position obtained by dividing the distance between the mask and the sample by the magnification ratio of the electron projecting lens. However, the maximum exposure area of the apparatus of this type is about several hundred xcexcm, and a lower throughput is obtained relative to the conventional optical exposure method. The factor that determines the exposure area is degradation in resolution due to off-axis aberrations of the electron projecting lens constructed by a magnetic doublet lens. The off-axis aberrations of the electron projecting lens mainly include curvature of field and astigmatism.
To remove the curvature of field of an electron projecting lens system, a technique has been proposed, which uses not an electron beam on the optical axis of the electron projecting lens system, but a charged particle beam shaped to have a sectional shape defined by two arcs about the optical axis, i.e., a charge particle beam having an arcuated section with which the influence of curvature of field of the electron projecting lens system becomes constant (Japanese Patent Laid-Open No. 10-135102).
FIG. 7 shows a conventional reduction transfer apparatus using an arcuated electron beam. An electron beam 2 emitted from an electron gun 1 forms an image on an aperture 4 for shaping the crossover image formed by the electron gun 1 into an arcuated beam. A transfer mask 8 placed on a mask stage 9 is uniformly irradiated with a beam 3 shaped into an arcuated shape through an electron reduction lens 6 and collimator lens 7 on the rear side. As the transfer mask 8, either a scattering type mask having a scattering pattern on the thin-film mask substrate that passes the electron beam for scattering the electron beam, or a stencil type mask having an absorbing pattern for shielding or attenuating the electron beam can be used. However, when the restriction or reduction ratio of the exposure pattern is taken into consideration, a scattering mask is more practical. In this case, a scattering transfer mask 8 is employed. A scattered electron limiting aperture 11 stops electron beams that have passed through the scattering pattern while allowing electron beams pass through portions without the scattering pattern, thereby irradiating a wafer 16 with an electron beam carrying pattern information.
The astigmatism which is the main aberration of electromagnetic lens sections 120 and 140 constructing the electron projecting lens is corrected by an astigmatism correction electrode 10. This correction electrode 10 has an arcuated slit. When a voltage is applied across the conductive thin film formed on the lower surface of the transfer mask 8 and the correction electrode 10, an electrostatic lens having a concave lens function with respect to the electron beam is formed in the radial direction.
The astigmatism correction electrode 10 has, in the radial direction of the electron projecting lens, a concave lens function with respect to the electron beam. For this reason, when the astigmatic axis of the astigmatism of the electron projecting lens (major axis of the elliptical blur of the electron beam due to the astigmatism and curvature of field) matches the direction of the concave lens function of the astigmatism correction electrode 10, the astigmatism can be corrected.
However, when the electron projecting lens is formed by a magnetic doublet (electron lens formed from two, front- and rear-side electromagnetic lens sections) used for an electron beam reduction transfer apparatus, the direction of the concave lens function of the electrostatic astigmatism corrector does not match the direction of the astigmatic axis of the astigmatism, as shown in FIG. 4. The reason for this is as follows. Since the electron beam is rotated in the magnetic doublet lens of a reduction system, anisotropic components of astigmatism (imaginary part of an astigmatic coefficient) are present, and the direction of the astigmatic axis of the electron projecting lens is different from the correction direction of the electrostatic astigmatism corrector. Hence, when an arcuated electron beam in which the optical axis of the electron projecting lens and the principal ray of the electron beam are offset is employed, it is difficult to correct the astigmatism of the electron projecting lens by the electrostatic astigmatism corrector.
The present invention has been made in consideration of the above problem of the prior art, and has as its object to provide an electron beam exposure apparatus having resolution and throughput higher than those of the prior art or an electron lens applicable to the apparatus and, more specifically, to reduce anisotropic components of the astigmatism of the electron lens of an electron beam exposure apparatus in which the optical axis of the electron projection lens system and the principal ray axis of the electron beam are offset, and to remove the astigmatism by a corrector such as an electrostatic astigmatism corrector.
According to a first aspect of the present invention, there is provided an electron beam exposure apparatus for drawing a pattern on a substrate while irradiating the substrate with an electron beam through an electron projecting lens, wherein the electron projecting lens has a magnetic doublet lens including a pair of electromagnetic lens sections, each constructed by a non-rotational lens.
In the electron beam exposure apparatus according to the first aspect of the present invention, the non-rotational lens serving as the electromagnetic lens section preferably comprises a pair of symmetrical electromagnetic lenses.
In the electron beam exposure apparatus according to the first aspect of the present invention, on-axis field distributions generated by the pair of electromagnetic lenses preferably have opposite polarities.
In the electron beam exposure apparatus according to the first aspect of the present invention, exciting currents supplied to the pair of electromagnetic lenses, preferably have substantially the same magnitude, but opposite directions.
In the electron beam exposure apparatus according to the first aspect of the present invention, preferably, exciting coils of the pair of electromagnetic lenses are wound in opposite directions, and the exciting coils of the electromagnetic lenses are series-connected.
In the electron beam exposure apparatus according to the first aspect of the present invention, exposure is preferably executed using an electron beam passing through an off-axis portion of the electron projecting lens.
In the electron beam exposure apparatus according to the first aspect of the present invention, exposure is preferably executed using an electron beam passing through an arcuated off-axis portion of the electron projecting lens.
The electron beam exposure apparatus according to the first aspect of the present invention preferably further comprises a corrector for correcting aberration of the electron projecting lens.
The electron beam exposure apparatus according to the first aspect of the present invention preferably further comprises an astigmatism corrector for correcting astigmatism of the electron projecting lens.
In the electron beam exposure apparatus according to the first aspect of the present invention, the astigmatism corrector preferably has a concave lens function in the radial direction of the electron projecting lens.
According to a second aspect of the present invention, there is provided a device manufacturing method comprising the steps of applying a resist to a substrate, drawing a pattern on the substrate to which the resist is applied, using an electron beam exposure apparatus, and developing the substrate on which the pattern is drawn, wherein the electron beam exposure apparatus draws the pattern on the substrate while irradiating the substrate with an electron beam through an electron projecting lens, the electron projecting lens having a magnetic doublet lens including a pair of electromagnetic lens sections, each constructed by a non-rotational lens.
According to a third aspect of the present invention, there is provided an electron lens comprising a magnetic doublet lens having two electromagnetic lens sections, each constructed by a non-rotational lens.
In the electron lens according to the third aspect of the present invention, the non-rotational lens serving as the electromagnetic lens section preferably comprises a pair of symmetrical electromagnetic lenses.
In the electron lens according to the third aspect of the present invention, on-axis field distributions generated by the pair of electromagnetic lenses preferably have opposite polarities.
In the electron lens according to the third aspect of the present invention, exciting currents supplied to the pair of electromagnetic lenses preferably have substantially the same magnitude, but opposite directions.
In the electron lens according to the third aspect of the present invention, preferably, exciting coils of the pair of electromagnetic lenses are wound in opposite directions, and the exciting coils of the electromagnetic lenses are series-connected.
Further objects, features, and advantages of the present invention will become apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings.